The present invention relates to implantable medical devices for stimulating body tissue and sensing body parameters (i.e., microstimulators and microsensors) as are known in the art. See, e.g., U.S. Pat. Nos. 5,193,539; 5,193,540; 5,312,439; 5,324,316; 5,358,514; and 5,405,367; each of which is incorporated herein by reference in its entirety. Generally, such implantable devices are referred to herein as microdevices.
Such implantable microdevices are characterized by a sealed housing which contains electronic circuitry for producing small electric currents between spaced electrodes (or sensing body parameters via the spaced electrodes). By precisely implanting the microdevices proximate to targeted tissue, the currents will stimulate the tissue or sense a physiological parameter and thus such devices produce medically beneficial results.
Typically, such microdevices derive operating power from an internal coil that is inductively coupled to an external AC magnetic field produced, for example, by a drive coil placed proximate to the microdevice(s). An AC voltage induced in the internal coil of the microdevice is rectified and filtered to produce a DC operating voltage which is used to power the electronic circuitry or power a battery contained within which in turn powers the electronic circuitry. Such an arrangement requires that the user remain in close proximity to the drive coil to maintain sufficient power transfer to operate the microdevice, e.g., to maintain tissue stimulation.
Alternatively, such microdevices can operate from power received from an internal rechargeable battery. See, e.g., U.S. Pat. Nos. 6,164,284; 6,185,452; 6,208,894; and 6,315,721; each of which is incorporated herein by reference in its entirety. Such battery-powered devices can, dependent upon the treatment regimen, be distributed throughout a patient's body. While such battery-powered devices free the user from always remaining in close proximity to the drive coil (to maintain operation of the device), each such rechargeable device still requires periodic charging.